The present invention relates to a method of manufacturing organopolysiloxanes, more particularly to a method of manufacturing an epoxy group-containing organopolysiloxane having a relatively high polymerization degree by a simple reaction which is not accompanied by cleavage of the oxirane ring of the epoxy group during the reaction. The invention further relates to a method for producing an organopolysiloxane which contains both epoxy and alkenyl groups and, therefore, can be effectively used as an epoxy group-containing silicone coating compound and as the epoxy group-containing silicone compound that constitutes the main ingredient of an addition reaction-type hardenable organopolysiloxane.
Epoxy group-containing organopolysiloxanes are used in numerous applications, such as fabric finishing agent, water repellent agent, modifier for resin material, etc. Especially, those having a relatively high polymerization degree are capable of imparting desired degrees of soft and pleasant feel to materials mixed therewith and are considered excellent fabric finishing agent because they do not cause the treated fabric to become excessively slimy and turn yellow, as fabric treated with aminosiloxane does.
Already various methods are known for manufacturing epoxy group-containing organopolysiloxanes, including those wherein an olefin group-containing siloxane is peroxidized, for example, vinylsiloxane is peroxidized in a 40%-acetyl hydroperoxide solution; a method wherein a siloxane which has been Grignard-reacted to introduce a .tbd.SiCH.sub.2 MgBr group into its molecule is epoxidated with alkali and epichlorohydrin; and a method wherein a chlorosilane or an acetoxylsilane is treated with glycidol to obtain glycidyl silicone ether (U.S. Pat. No. 2,730,532). All of these methods are poor in yield (only 20% in the first method), require complicated process conditions, and are not consistent in the production results. Furthermore, although these methods are suitable for epoxidating silane and low molecular weight siloxanes, they do not work well when epoxidizing relatively high molecular weight siloxanes due to various limitations in reaction conditions. A problem with the '532 patent method is that the resulting organosiloxane is readily hydrolyzed or alcoholized due to the presence therein of an epoxy organo group bonded to Si atom via an ether linkage, so that the product is extremely unstable.
As a method for manufacturing epoxidated organopolysiloxane of high molecular weight, a method was proposed (U.S. Pat. No. 3,431,143) wherein an unsaturated epoxy monomer and an organohydrogenpolysiloxane containing an Si-bonded hydrogen atom(s) undergo an addition reaction in the presence of a peroxide or a Pt-containing catalyst. This method requires relatively simple reaction conditions and gives high yields; but when the method is employed to obtain a product of relatively high polymerization degree, control of the reaction becomes difficult, and it is also difficult to prepare the starting organohydrogenpolysiloxane of a high polymerization degree, so that the manufacture flow becomes complicated and time-consuming to the extent that the manufacturing cost becomes too high. Furthermore, with this method it is impossible to make an epoxy group-containing organopolysiloxane having alkenyl as a group or attached to a side chain, which is a useful main ingredient of an addition reaction-type hardenable organopolysiloxane. In order to make this organopolysiloxane, if an addition reaction is caused to occur between an alkenyl-containing organohydrogenpolysiloxane and an unsaturated epoxy monomer, an undesirable addition between the hydrogen attached to a Si atom and the alkenyl proceeds to form a gel.
A method is known for the production manufacture of an organosiloxane wherein an organosiloxane is produced from low molecular weight organosiloxane such as a cyclic siloxane through a siloxane rearrangement equilibration reaction in the presence of a strongly acidic or basic compound as a catalyst. However, since an epoxy group is easily attacked by acid, an acid catalyst cannot be used in the equilibration of the epoxy group-containing siloxane, and if a base catalyst is employed, the equilibration with the siloxane having an epoxy group is so slow that cleavage of the oxirane ring of the epoxy group occurs more readily.
It is known that the equilibration of an organopolysiloxane is facilitated through an addition of a small amount of certain polar solvents. It is also known that a siloxane rearrangement equilibration reaction occurs with a mixture of octamethylcyclotetrasiloxane and hexamethyldisiloxane in tetrahydrofuran in the presence of a strongly basic compound such as potassium hydroxide as a catalyst. However, these reactions are not practical because the presence of even an extremely small amount of an impurity will adversely affect the reaction.
To manufacture an organopolysiloxane in the presence of a base catalyst, a method is proposed wherein the reaction rate is increased by the addition of an alkylsulfoxide, such as dimethylsulfoxide (U.S. Pat. No. 3,175,995). However, cleavage of the epoxy ring reduces the yield of the desired organopolysiloxane. Moreover, these organic solvents have high melting points and dimethylsulfoxide, because of its low melting point, is a solid during the winter season. Therefore, they are not easy to handle, and their high boiling point make them difficult to separate after the reaction so that their characteristic smell remains in the product. Furthermore, when the thus produced siloxane is used together with other resin in a fabric treatment, discoloration occurs and the stability of the treatment liquid becomes low.
A method is also known wherein an organopolysiloxane saturated with water (an amount of less than one weight % is equilibrated in the presence of a base catalyst to thereby obtain an epoxy group-containing siloxane of relatively low molecular weight which retain uncleaved the oxirane rings of the epoxy groups (Japanese Patent Kokoku No. 51-33839). Although the equilibration rate is improved by this method, it is not possible to prevent cleavage of the oxirane rings of epoxy group by the water and the presence of water also produces silanol groups at the ends of the siloxane molecule during the equilibration reaction which stops the growth of the siloxane chain. It thus becomes difficult to obtain high molecular weight polymers and also, since the distribution range of polymerization degree of the product polymers becomes wide, molecular weight control becomes difficult. Thus, reproducing the same polymer is very difficult. Furthermore, after the equilibration, when the product is neutralized and stripped of the unreacted low molecular siloxane, the amount of the hydroxyl contained in the product changes, causing the viscosity to vary greatly so that it is difficult to control the viscosity.